[/ Boost.Optional Copyright (c) 2015 - 2018 Andrzej Krzemienski Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) ] [section:relnotes Release Notes] [heading Boost Release 1.69] * Remove deprecation mark from `reset()` method (without arguments). * Fixed [@https://github.com/boostorg/optional/issues/59 issue #59]. * Fixed bug with initialization of certain wrapper types in clang with -std=c++03. See [@https://github.com/boostorg/optional/pull/64 pr #64]. [heading Boost Release 1.68] * Added member function `has_value()` for compatibility with `std::optional` ([@https://github.com/boostorg/optional/issues/52 issue #52]). * Added member function `map()` for transforming `optional` into `optional` using a function of type `T -> U`. * Added member function `flat_map()` for transforming `optional` into `optional` using a function of type `T -> optonal`. [heading Boost Release 1.67] * Fixed [@https://github.com/boostorg/optional/issues/46 issue #46]. * Fixed `-Wzero-as-null-pointer-constant` warnings. [heading Boost Release 1.66] * On newer compilers `optional` is now trivially-copyable for scalar `T`s. This uses a different storage (just `T` rather than `aligned_storage`). We require the compiler to support defaulted functions. * Changed the implementation of `operator==` to get rid of the `-Wmaybe-uninitialized` false-positive warning from GCC. [heading Boost Release 1.63] * Added two new in-place constructors. They work similarly to `emplace()` functions: they initialize the contained value by perfect-forwarding the obtained arguments. One constructor always initializes the contained value, the other based on a boolean condition. * Syntax `o = {}` now correctly un-initializes optional, just like in `std::optional`. * Fixed [@https://svn.boost.org/trac/boost/ticket/12203 Trac #12203]. * Fixed [@https://svn.boost.org/trac/boost/ticket/12563 Trac #12563]. [heading Boost Release 1.62] * Fixed [@https://svn.boost.org/trac/boost/ticket/12179 Trac #12179]. [heading Boost Release 1.61] * Now `boost::optional` is specialized for reference parameters. This addresses a couple of issues: * the `sizeof` of optional reference is that of a pointer, * some bugs connected to copying optional references are gone, * all run-time bugs caused by incorrect reference binding on some compilers are now turned into compile-time errors, * you can swap optional references: it is like swapping pointers: shalow, underlying objects are not affected, * optional references to abstract types work. * Documented nested typedefs ([@https://svn.boost.org/trac/boost/ticket/5193 Trac #5193]). * Made the perfect-forwarding constructor SFINAE-friendly, which fixes [@https://svn.boost.org/trac/boost/ticket/12002 Trac #12002]. However, this only works in the newer platforms that correctly implement C++11 ``. * Fixed [@https://svn.boost.org/trac/boost/ticket/10445 Trac #10445]. [heading Boost Release 1.60] * Changed the implementation of `boost::none` again. Now it is a const object with internal linkage (as any other tag). This fixes [@https://svn.boost.org/trac/boost/ticket/11203 Trac #11203]. [heading Boost Release 1.59] * For C++03 compilers, added 0-argument overload for member function `emplace()`, and therewith removed the dependency on ``. * Fixed [@https://svn.boost.org/trac/boost/ticket/11241 Trac #11241]. [heading Boost Release 1.58] * `boost::none_t` is no longer convertible from literal `0`. This avoids a bug where `optional> oi = 0;` would initialize an optional object with no contained value. * Improved the trick that prevents streaming out `optional` without header `optional_io.hpp` by using safe-bool idiom. This addresses [@https://svn.boost.org/trac/boost/ticket/10825 Trac #10825]. * IOStream operators are now mentioned in documentation. * Added a way to manually disable move semantics: just define macro `BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES`. This can be used to work around [@https://svn.boost.org/trac/boost/ticket/10399 Trac #10399]. * It is no longer possible to assign `optional` to `optional` when `U` is not assignable or convertible to `T` ([@https://svn.boost.org/trac/boost/ticket/11087 Trac #11087]). * Value accessors now work correctly on rvalues of `optional` ([@https://svn.boost.org/trac/boost/ticket/10839 Trac #10839]). [heading Boost Release 1.57] * [@https://github.com/boostorg/optional/pull/9 Git pull #9]: ['"Supply `` to fix C++03 compile error on `logic_error("...")`"]. [heading Boost Release 1.56] * Added support for rvalue references. Now `optional` works with moveable but non-copyable `T`'s, * Improved `swap` (now uses move operations), * Added function `emplace()`. This is the last of the requests from [@https://svn.boost.org/trac/boost/ticket/1841 Trac #1841], * `optional` is moveable, including conditional `noexcept` specifications, which make it `move_if_noexcept`-friendly, * Using explicit operator bool() on platforms that support it ([@https://svn.boost.org/trac/boost/ticket/4227 Trac #4227]) (breaking change), * Forward declaration of `operator<<(ostream&, optional const&)` to prevent inadvertent incorrect serialization of optional objects, * Removed deprecated function `reset()` from examples ([@https://svn.boost.org/trac/boost/ticket/9005 Trac #9005]), * Equality comparison with `boost::none` does not require that `T` be EqualityComparable, * Optional rvalue references are explicitly disallowed, * Binding temporaries to optional references is explicitly disallowed (breaking change), * More ways to access the contained value, functions `value()`, `value_or()`, `value_or_eval()`, * Updated and reorganized documentation, added tutorial and quick guide sections. 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